Acoustic pulse response measuring

Abstract

A sound source located inside a tube having one end inside the mouth or nose of a subject provides an acoustic transient signal that propagates into the respiratory system of the subject to provide reflections sensed by a single mircophone inside the tube between the sound source and the mouth of the subject for recording on a transient recorder or computer and display on an oscilloscope after passing through a low pass filter to provide an output signal representative of the acoustical properties of the airways of the subject. This output signal may be processed in accordance with the deconvolution integral and other algorithms to determine essentially the acoustic impulse response, impedance or effective cross-sectional area of the airways, typically as a function of the distance from a reference point, such as the end of the tube.

What is claimed is: 
     
       1. Apparatus for measuring physical properties of a confined volume comprising, conduit means for exchanging acoustical energy with said confined volume,   means for propagating a pressure pulse within said conduit through an opening thereof for entry into the confined volume,   electroacoustical transducing means in said conduit responsive to acoustical energy therein for providing an electrical signal representative of wave energy having spectral components in a substantial portion of the audio frequency range above 100 Hz reflected through said opening in response to said pressure pulse propagated through said opening provided by said means for propagating,   and utilization means responsive to said detected signal for providing a representation thereof characteristic of physical properties of said confined volume,   said physical properties including the cross sectional area of said confined volume as a function of its distance from said opening.   
     
     
       2. Apparatus in accordance with claim 1 wherein said means for propagating comprises a sound source inside said conduit means. 
     
     
       3. Apparatus in accordance with claim 1 and further comprising said confined volume connected to said opening. 
     
     
       4. Apparatus in accordance with claim 1 wherein said conduit means has a second opening with the distance between said second opening and said electroacoustic transducing means being greater than the distance between said electroacoustic transducing means and the furthest point of interest in said confined volume, whereby reflected wave energy from said confined volume enters said first-mentioned opening and arrives at said electroacoustic transducing means before wave energy reflected from the second-mentioned opening.   
     
     
       5. Apparatus for measuring physical properties of a confined volume in accordance with claim 1 wherein said electroacoustical transducing means comprises a single microphone. 
     
     
       6. Apparatus for measuring physical properties of a confined volume in accordance with claim 1 and further comprising, means for injecting into said confined volume prior to propagating said pressure pulse a mixture of a gas having a density less than that of air with oxygen. 
     
     
       7. Apparatus for measuring physical properties in accordance with claim 6 wherein said gas is helium. 
     
     
       8. Apparatus for measuring physical properties of a confined volume in accordance with claim 7 wherein said mixture is substantially 80% helium and 20% oxygen. 
     
     
       9. A method of measuring physical properties of a confined volume which method includes the steps of, connecting the opening of a conduit to an entrance to said confined volume,   propagating a pressure pulse inside said conduit through said opening,   and detecting wave energy having spectral components in a substantial portion of the audio frequency range above 100 Hz reflected through said opening as it arrives at electroacoustical transducing means in said conduit to provide an electrical signal representative of physical characteristics of said confined volume connected to said opening, said physical characteristics including the cross sectional area of said confined volume as a function of the cross sectional area distance from said opening.   
     
     
       10. A method in accordance with claim 9 wherein said entrance is the mouth of a subject and further including the steps of processing said electrical signal to provide a visual representation of airway cross sectional area as a function of distance from the mouth. 
     
     
       11. A method in accordance with claim 10 and further including the step of uttering phonemes and observing said visual display. 
     
     
       12. A method in accordance with claim 10 and further including the step of injecting a mixture of a gas having a density less than that of air with oxygen through said mouth before propagating said pressure pulse. 
     
     
       13. A method in accordance with claim 12 wherein said gas is helium. 
     
     
       14. A method in accordance with claim 13 wherein said mixture is substantially 80% helium and 20% oxygen.